It is well known that an evacuated article or element, i.e. an article which has substantially all of the air removed from its interior volume, is desirable for use as insulation, because convection heat loss for such an article is almost zero. Other desirable characteristics of insulation in general include low conduction heat and low radiation heat loss. Reduction of conduction heat loss is typically accomplished by decreasing the material to material contact to an amount which is just sufficient to maintain structural integrity of the article, while radiation heat loss is typically minimized by the use of interior reflective surfaces.
While evacuated insulation typically has good convection heat transfer characteristics, i.e. low convection heat loss, it is also typically quite expensive and relatively slow and difficult to manufacture. Further, the amount of internal material contact is often an issue with such insulation, because of the resulting increase in conductive heat loss, because substantial internal support is necessary to maintain the structural integrity of the evacuated article against the differential of the internal and external pressure. U. S. Patent No. 3,936,553 to Rowe is illustrative of evacuated insulation which includes a plurality of transverse support pins within the interior volume of the article and insulating material at the edges of the article to maintain the integrity of the insulation. Such insulation is, however, expensive to manufacture, and thus not extensively used.
The present invention is directed toward a article of insulation, as well as a corresponding method for manufacturing such an article, which is evacuated and thus has all of the advantages of evacuated insulation, but which is relatively inexpensive to manufacture and which also has a relatively low conduction and radiation heat loss.